The present disclosure relates to an electronic device, connection detection method and connection detection system and, more particularly, to an electronic device capable of quickly detecting the disconnection from the camera main body, and a connection detection method used by the same and connection detection system having the same.
Some cameras are used with a replacement lens connected to the camera main body (e.g., Japanese Patent Laid-Open No. 2007-101656 hereinafter referred to as Patent Document 1).
In the camera disclosed in Patent Document 1, all the terminals other than the power terminal are disconnected first, followed finally by the disconnection of the power terminal at the time of detachment of a replacement lens from the camera main body so as to stabilize the electrical connection between the camera main body and replacement lens.
On the other hand, a camera having a configuration as illustrated in FIG. 1 is also known to detect the connection status of a replacement lens. A camera 200 shown in FIG. 1 includes a camera main body 201 and a replacement lens 202 that is connected as necessary to the camera main body 201.
The camera main body 201 includes a power terminal 211, a detection terminal 212, a battery 213, resistors 214-1 to 214-3, a field effect transistor 215, an operational amplifier 216 and a microcomputer 217.
When the replacement lens 202 is attached to the camera main body 201, the power terminal 211 and detection terminal 212 of the camera main body 201 come into contact respectively with a power terminal 231 and a detection terminal 232 of the replacement lens 202.
DC voltage is supplied from the battery 213 to the replacement lens 202 as a result of the power terminal 211 coming into contact with the power terminal 231.
The camera main body 201 uses a detection circuit 221 to detect the connection or disconnection of the detection terminals 212 and 232.
In the example shown in FIG. 1, the detection circuit 221 includes the resistors 214-1 and 214-2, the field effect transistor 215 and the operational amplifier 216.
The output voltage of the operational amplifier 216, i.e., the input voltage to the microcomputer 217, changes with change in the gate voltage of the field effect transistor 215 connected to the detection terminal 212.
The microcomputer 217 detects the change in this input voltage, thus detecting the connection or disconnection of the replacement lens 202 to or from the camera main body 201.
A description will be given next of a connection detection circuit of the replacement lens 202. The replacement lens 202 includes the power terminal 231, the detection terminal 232, a resistor 233, a disconnection voltage detector 234, a microcomputer 235, a reset voltage detector 236 and a capacitor 237.
The replacement lens 202 uses the disconnection voltage detector 234 to detect the connection or disconnection of the replacement lens 202 to or from the camera main body 201.
When the disconnection voltage detector 234 determines that the input voltage is greater than a predetermined threshold voltage, the disconnection voltage detector 234 pulls the output voltage to the microcomputer 235 up to high level. If the disconnection voltage detector 234 determines that the input voltage is smaller than the predetermined threshold voltage, the disconnection voltage detector 234 pulls the output voltage to the microcomputer 235 down to low level.
The microcomputer 235 detects the high-to-low transition of the output voltage from the disconnection voltage detector 234, i.e., the input voltage to the microcomputer 235, thus detecting the disconnection from the camera main body 201.
On the other hand, the replacement lens 202 uses the reset voltage detector 236 to detect the timing when the microcomputer 235 is reset.
The reset voltage detector 236 detects a predetermined threshold voltage (e.g., guaranteed operating voltage) smaller than the predetermined threshold voltage detected by the disconnection voltage detector 234.
Further, when the reset voltage detector 236 determines that the input voltage is greater than the predetermined threshold voltage, the reset voltage detector 236 pulls the output voltage to the microcomputer 235 up to high level. If the reset voltage detector 236 determines that the input voltage is smaller than the predetermined threshold voltage, the reset voltage detector 236 pulls the output voltage to the microcomputer 235 down to low level.
The microcomputer 235 performs a reset when the microcomputer 235 detects the high-to-low transition of the output voltage from the reset voltage detector 236.
The capacitor 237 is charged with the DC voltage supplied from the battery 213 when the replacement lens 202 is connected to the camera main body 201. The capacitor 237 supplies power based on the charge stored therein to the microcomputer 235 only for a predetermined period of time after the replacement lens 202 is disconnected from the camera main body 201.
FIGS. 2A to 2D illustrate the timing at which the connection status is detected by the replacement lens 202 in the past.
FIG. 2A illustrates the voltage of the power terminal 231. A constant DC voltage is supplied from the battery 213 of the camera main body 201 to the power terminal 231 until the camera main body 201 is disconnected.
When the camera main body 201 is disconnected, the power terminal 231 is detached from the power terminal 211, thus allowing for the voltage stored in the capacitor 237 to be supplied to the power terminal 231.
The charge stored in the capacitor 237 decreases gradually because of its consumption by the microcomputer 235. This leads to a gradual decline in the voltage of the capacitor 237, and therefore, the voltage supplied to the microcomputer 235.
FIG. 2B illustrates the physical connection between the camera main body 201 and replacement lens 202. In FIG. 2B, the low level indicates the connection of the replacement lens 202 to the camera main body 201, and the high level indicates the disconnection of the replacement lens 202 from the camera main body 201.
FIG. 2C illustrates the input voltage of the microcomputer 235, i.e., the output voltage from the disconnection voltage detector 234. When the replacement lens 202 is disconnected from the camera main body 201, the voltage of the power terminal 231 declines gradually as illustrated in FIG. 2A.
The disconnection voltage detector 234 changes the output voltage to the microcomputer 235 from high to low level if the voltage of the power terminal 231 drops to the predetermined threshold voltage (i.e., disconnection voltage).
The microcomputer 235 detects the change in the input voltage from the disconnection voltage detector 234, thus detecting the disconnection of the replacement lens 202 from the camera main body 201.
FIG. 2D illustrates a period of time t′ during which a termination process is performed. The termination process is performed within a period of time t from the detection of the disconnection to the detection of a reset voltage by the microcomputer 235.
As described with reference to FIG. 1, the reset voltage detector 236 changes the output voltage to the microcomputer 235 from high to low level if the voltage of the power terminal 231 drops to the predetermined threshold voltage (i.e., reset voltage).
The microcomputer 235 detects the change in the input voltage from the reset voltage detector 236, thus detecting the decline of the voltage to the reset voltage.
The termination process is designed specifically to stop the actuator adapted to drive the lens area of the replacement lens 202.
This makes it possible to safely stop the replacement lens 202 even if the replacement lens 202 is abruptly disconnected from the camera main body 201.